The present invention relates to quinolone carboxylic acids, derivatives thereof, and methods of making and using the same. In particular, the present invention relates to fluoroquinolone carboxylic acids, derivatives thereof, methods of making and using the same.
Bacterial pathogens continue to pose a serious threat to public health as indicated by a worldwide resurgence of bacterial diseases. One aspect of this resurgence appears to be the result of prior widespread, and largely effective, therapeutic and prophylactic use of antibiotics, which, unfortunately, over time has also selected for resistant strains of various bacterial pathogens. Of particular concern to the public health has been the emergence and proliferation of bacterial strains that are resistant to multiple antibiotics in the current arsenal of antimicrobial agents. Such multiantibiotic-resistant (“MAR”) bacterial strains include species of Gram-positive bacteria, such as, antibiotic-resistant strains of Staphylococcus aureus, Enterococcus fecalis, and Enterococcus fecium, which, along with antibiotic-resistant Gram-negative strains of Escherichia coli, constitute the most frequent etiological agents of nosocomial (hospital-acquired) diseases, such as septicemia, endocarditis, and infections of wounds and the urinary tract. S. aureus is currently the most frequent cause of nosocomial bacteremia and skin or wound infection. Streptococcus pneumoniae causes several serious and life-threatening diseases, including a contagious meningitis, bacteremia, and otitis media. Annual mortality from S. pneumoniae infection alone is estimated at between 3-5 million persons globally. More recently, clinical accounts of highly aggressive skin and tissue infections by “flesh-eating” strains of Group-A streptococcus bacteria, such as Streptococcus pyogenes, has heightened the concern and need for new or improved antibacterial agents.
Quinolones constitute a group of antibiotics that have been available since the early 1960s and have proved to be valuable antibacterial agents. Quinolone carboxylic acid derivatives having various chemical structures have been synthesized, developed, and marketed. Nalidixic acid (1,4-dihydro-1-ethyl-7-methyl-1,8-naphthyridin-4-one-3-carboxylic acid), the progenitor of the series, was used primarily as a urinary-tract antiseptic. Later development provided agents with broader activity, increased potency against selected pathogens and improved pharmacokinetic and pharmacodynamic properties.
From a medical utility viewpoint, the quinolones are classified as first-, second-, and third-generation compounds. First-generation compounds like piromidic acid (8-ethyl-5,8-dihydro-5-oxo-2-(1-pyrrolidinyl)pyrido(2,3-d)pyrimidine-6-carboxylic acid) and pipemidic acid (8-ethyl-5,8-dihydro-5-oxo-2-(1-piperazinyl)pyrido(2,3-d)pyrimidine-6-carboxylic acid) provided coverage for Gram-negative Enterobacteriaceae. The second-generation compounds are divided into those with enhanced but predominant Gram-negative activity, against pathogens like Escherischia coli and Pseudomonas aeruginosa, and those with balanced broad-spectrum activity (norfloxacin, pefloxacin, enoxacin, fleroxacin, lomefloxacin, ciprofloxacin, ofloxacin, rufloxacin, nadifloxacin). Norfloxacin, ofloxacin, and ciprofloxacin have, therefore, been used mainly for treatment of diseases including urinary tract infections, gastrointestinal infections, sexually transmitted diseases and the like. Third-generation antibiotics (levofloxacin, pazufloxacin, sparfloxacin, clinafloxacin, sitafloxacin, trovafloxacin, tosufloxacin, temafloxacin, grepafloxacin, balofloxacin, moxifloxacin, gatifloxacin) are those with enhanced activity against Gram-positive cocci (notably clinafloxacin, sitafloxacin, trovafloxacin for Streptococcus pneumoniae) and, for essentially all the third-generation quinolones, activity also against Gram-negative Haemophilus influenzae and Legionella pneumophila, and against anaerobes and atypical pathogens. Levofloxacin, moxifloxacin, and gatifloxacin have, therefore, found use for community-acquired infections such as those of the upper and lower respiratory tract infections (“RTI”) like pneumonia, sinusitis and pharyngitis, and for skin and soft tissue infections (“SSI”) caused by Gram-positive strains of staphylococci, pneumococci, streptococci, and enterococci. 
The improvements seen in most of the third-generation antibiotics in current use are generally attributed to their uniqueness in inhibiting DNA gyrase and topoisomerase IV of the bacterial targets. Three categories of quinolone inhibition have been suggested. Type I quinolones (norfloxacin, enoxacin, fleroxacin, ciprofloxacin, lomefloxacin, trovafloxacin, grepafloxacin, ofloxacin and levofloxacin) indicate a preference for topoisomerase IV inhibition. Type II quinolones (nadifloxacin and sparfloxacin) indicate a preference for DNA gyrase inhibition. Type III quinolones to which some of the third-generation quinolones belong (e.g., gatifloxacin, pazufloxacin, moxifloxacin and clinafloxacin) display, however, a dual-targeting property, and equally influence DNA gyrase inhibition and topoisomerase IV inhibition. (M. Takei, et al., Antimicrobial Agents and Chemotherapy, Vol. 45, 3544-49 (2000)). DNA gyrase is the primary target in bacteria, and thus is explained the weaker activity in Gram-positive bacteria of the topoisomerase IV-targeting second-generation quinolones like norfloxacin, ciprofloxacin, ofloxacin, and levofloxacin. The unusual activity of nadifloxacin described in the literature, especially against Gram-positive S. aureus, now can be explained by its ability to target DNA gyrase (N. Oizumi, et al., J. Infect. Chemother., Vol. 7, 191-194 (2001)). That some third-generation quinolones are primarily capable of targeting topoisomerase IV in Gram-positive staphylococci, and DNA gyrase in Gram-positive S. pneumoniae, explains the advantages provided by the dual-targeting third-generation quinolones like moxifloxacin and gatifloxacin. However, because of continuing threat of new strains of antibiotic-resistant bacteria that may surface in the future, continued effort has been devoted to develop new broad-spectrum antibiotics.
A family of fluoroquinolones was recently developed, and some compounds of this family show good antimicrobial activity against a wide range of Gram-positive and Gram-negative bacteria. See U.S. Pat. Nos. 5,385,900; 5,447,926; 6,685,958; and 6,699,492; all of which are incorporated herein by reference in their entirety. Because of the promise of their therapeutic value, it is very desirable, in one aspect, to develop improved processes for preparing this family of fluoroquinolones in order to allow for a more widespread availability of these compounds.